1. Field of the Invention
The present invention relates to a weight for a hard contact lens and a hard contact lens composite employing such a weight. More particularly, it relates to a soft or flexible weight for a hard contact lens, which is designed to be attached to the peripheral edge of a hard contact lens, particularly a multi-focal hard contact lens, to improve the stability of the lens and the comfortableness to the wearer, and a hard contact lens composite employing such a weight.
2. Description of the Background
Heretofore, a hard contact lens, particularly a multi-focal hard contact lens, has had a problem that the positioning of the lens tends to be instable because of its special design. Under the circumstances, various proposals have been made to improve the stability by various lens designs (JP-A-7-239459, JP-A-6-34920, Japanese Patent No. 2539531, JP-A-4-212925 and JP-A-3-107817). However, none of them provides adequate stability.
Further, there have been cases where a patient gives up wearing a hard contact lens, because the hard contact lens is poor in comfortableness to the wearer as compared with a soft contact lens, or a patient stops wearing a hard contact lens because of a miner problem on the cornea, such as 3-9 stain. Under the circumstances, it was proposed to improve the comfortableness to the wearer of a hard contact lens by making the periphery of the lens to be soft (JP-A-3-92336, and JP-A-4-45420). However, such a lens was difficult to produce and thus had a problem that its cost was high. Further, it had an optical problem that its optical region became narrow.
It was also proposed to attach a soft edge to a hard contact lens by polymerization or bonding (JP-A-49-120655, and JP-Y-40-1455). However, it was rather difficult to bond different types of materials, whereby there was a problem of costs, or a problem of poor optical properties. Further, it was proposed to detachably attach a hard contact lens on the outer surface of a soft contact lens base (JP-U-49-95955, JP-U-52-52955, and JP-U-53-22337). However, there were drawbacks such that the center thickness increased, and the oxygen permeability was hindered by the base, so that no adequate oxygen permeability was expected. Furthermore, a composite contact lens was proposed wherein instead of the base, an opening was provided at the center, and an optical member made of inorganic glass was fitted in the opening (JP-A-57-11652). However, as the optical member to be used, a currently available commercial product could not be used, and it had to be separately produced as a special part, thus leading to a problem that the production cost tended to be high.